Oxidation-resistant lubricating greases containing inorganic alkali metal compounds of high alkalinity



OXIDATION-RESISTANT LUBRICATING GREASES CONTAINING INORGANIC ALKALI METAL COB/[POUNDS OF HIGH ALKALINITY Lorne W. Sproule, Sarnia, Ontario, James H. Norton,

Corunna, Ontario, and Warren C. Pattenden, Courtright, Ontario, Canada, assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application August 12, 1954 Serial No. 449,528

4 Claims.. (Cl. 252-18) The present invention relates to improved oxidationresistant lubricating greases and to methods of preparing the same. The invention also relates to substantially anhydrous organic oleaginous materials, the oxidation-resistance of which is improved by the addition of the greases of the present invention.

In brief compass, the invention pertains to greases thickened to a grease consistency with a thickener containing a high proportion, preferably a major proportion, based on thickener, of a substantially oil-insoluble basic inorganic oxidation-inhibiting alkali metal compound having an original alkalinity of at least 21.5% Na O (as determined by the A.S.T.M. D-501-49 test). The poly-alkali metal salts of inorganic polybasic oxygen acids of silicon and phosphorus are preferred for the purposes of the invention.

Prior to the present invention it has been found that the poly-alkali metal phosphates and silicates of which trisodium phosphate is an outstanding example, have excellent oxidation-inhibiting characteristics when added to various organic materials, such as lubricating oils, of mineral and/or synthetic origin, fatty oils, greases, asphalts, etc. Also, lithium hydroxide has been recommended as an oxidation-inhibitor for lithium stearateand hydroxy stearate-greases. One of the prerequisites of the efiectiveness of these oxidation-inhibitors is, of course, a substantial chemical inertness of the inhibitor toward the material to be protected against oxidation, so that no undesirable reaction between these materials will destroy or detrimentally change the one or the other.

For example, it has been found that the alkaline inhibitors mentioned above may be added to mineral oil base soda and lithium soap greases with good success either during grease manufacture or to the finished greases. However, when it was attempted to add lithium hydroxide or trisodium phosphate to lime soap bases, or even to mixed lithium-lime soap greases during the manufacturing stage, calcium metal was replaced in the soap by lithium, completely changing the character of the soap. Complicated milling procedures had to be employed in these and similar cases to incorporate the inhibitor into the finished grease.

Difiiculties of equal magnitude may arise when the basic inorganic oxidation inhibitors are incorporated into certain synthetic oil base lubricating greases, independent of the type of thickener used. Many of the synthetic lubricating oils, particularly those of the dibasic acid ester and complex ester type, enter into undesirable side reactions with the alkaline inhibitors particularly at elevated temperatures and/or in the presence of appreciable amounts of water.

Also, in many cases it is difficult, if not impossible, to dissolve or adequately to disperse the inorganic inhibitor in mineral, fatty or synthetic oils as such. Thorough milling must be employed in these cases frequentlycomhigh temperature greases.

The present invention overcomes the aforementioned difiiculties and affords various additional advantages. It is, therefore, an object of the present invention to provide for an improved method of increasing the oxidation resistance of organic oleaginous materials. Another object of the invention is to provide improved compositions containing basic inorganic compounds as oxidation inhibitors. Other and more specific objects and advantages of the invention will appear from the description given hereinafter.

The present invention is based on the discovery that oil-insoluble inorganic base alkali metal compounds having oxidation-inhibiting characteristics may be readily incorporated into metal soap-thickened mineral oil base greases in large proportions of as much as 50% by weight or more in the course of the manufacturing stage of the grease. More specifically, the mole ratio of inorganic inhibitor to soap should be at least 1 and may be as high as 10-20. The proportions of soap and inorganic compounds may be so chosen that a grease results which is thickened with an essentially inorganic type of grease thickener containing a small quantity of metal soap acting as a dispersing agent for the inorganic alkali metal compound in the dispersant oil.

Greases so prepared have good structure, smooth appearance and excellent high temperature stability in addition to exceptionally high oxidation resistance. They may be used as such for purposes normally requiring However, these greases find their greatest utility as oxidation-inhibiting additives for other greases or various oleaginous organic materials in which the inorganic alkali metal compounds cannot be readily dispersed as such for the reasons set forth above. This utility isbased on the surprising discovery that the greases of the invention are fully compatible with and readily dispersable in most organic oleaginous media without the need of arduous milling procedures.

It has also been found that the greases of the invention may be incorporated into oleaginous materials 'without detrimental side effects at conditions at which addition of the inorganic alkali metal compound inhibitor as such was found to be prohibitive as the result of undesirable side reactions. For example, the greases of the invention may be added in oxidation-inhibiting proportions to virtually all conventional grease stocks in any stage of the grease-making process. Also, the full benefit of the oxidation-inhibiting quality of the inorganic alkali metal compounds may be secured when the greases of the invention are added in oxidation-inhibiting proportions to such fatty or synthetic oils or compositions containing the same, as normally are reactive with the inorganic alkali metal compounds at conditions of preparation or use. Furthermore, the greases of the invention may serve to introduce oxidation-inhibiting proportions of the inorganic alkali metal compounds into liquid oleaginous materials without the use of additional solubilizer or dispersing aids.

The invention is broadly applicable to all inorganic alkali metal compounds of the proper alkalinity to exert an oxidation inhibiting effect on organic oleaginous materials which form carboxylic acids when undergoing oxidation by air. It has been found that an original alkalinity of the alkali metal compound of at least about 21.5% Na O is desirable for a prolonged oxidationinhibiting effect. The compounds of most universal utility and consistently highest efficiency comprise the polyalkali metal salts of inorganic polybasic oxygen acids of silicon and phosphorus and, more particularly, the

sodium and potassium salts of this type. By poly-metal stantially oil-insoluble.

metal salts are the ortho-and pyro-phosphates and the salts is meant those having at least two alkali metal atoms attached to a polybasic acid group. These salts are sub- Examples of suitable alkali ortho-, sesqui-, diand meta-silicates.

While the exact mechanism of-this inhibition is not clearly understood, it appears that ordinary oxidation in air, of most oleaginous materials, e.g. of lubricating oils reaction of'the basic salts with carbon dioxide present,

in the reaction medium or in the surrounding air.

The choice of salts varies somewhat with thetemper-t,

ature range for which stabilization is most important. In general, the alkali metal phosphates and silicates are 1 most suitable for high temperatureservice, e.g. ,for temperatures from about 200 to about 400 F. or higher,

because they are capable of decomposing stepwise in the.

presence of mineral oils to salts of lower metal content and alkalinity. Bases which react with CO in preference I to any reaction with other organic acids, such has most.

alkali and alkaline earth metal hydroxides, are-much .less.

fore they can react with the other organic acids,.and car: bonates are less efficient oxidation inhibitors. However,

satisfactory because they are converted to carbo'natesbelithium hydroxide has been found particularly effective as an inhibitor for lithium greases. In many applications,

the use of trisodiumphosphate is criticalfor optimumresults.

The liquid dispersant'used in the grease-inhibitor con-"- centrates of the invention should be an oil of lubricating 1 grade which is chemically substantially inert toward the inhibitor compound used. Mineral oil base lubricating, oils having a viscosity of at least 30 SSU at 100 F. are most suitable for this purpose. Certain synthetic hydrocarbon materials of lubricatingoil grade derived from various conventional polymerization and/ or alkylation processes or from the products of the' distillation and/o'r hydrogenation of carbonaceous solids, the catalytic synthesis of hydrocarbons from carbon monoxide and hy-- drogen, etc. may likewise be used. Substituted hydrocarbonaceous materials, such as oxygen, halogen, nitrogen, sulfur and/or phosphorus derivativesof the abovementioned materials, including fatty oils and fats, such as lard oil, sperm oil, etc. and their sulfur-containing derivatives, may form all or part of the grease dispersant.

A class of oleaginous materials which may serve as the dispersant of the greases of the invention comprises many synthetic oils of lubricating grade and viscosity 30 SSU at 100 F.), particularly when combined with varying proportions of the mineral oils described above. I

Examples of synthetic oils include ether alcohols, such as those corresponding to the formula RO(C,,H ,,O) H wherein R is an alkyl group, for example butyl, n is 'an integer from 15, for example 3, and x is greater than- 1, for example 14; esters of monobasic carboxylic acids; totaling 20-130 carbon atoms, such as those of C C aliphatic acids with C -C aliphatic alcohols, theC C radicals including the butyl, isobutyl, hexyl, octyl, 'iso-- octyl,'2-ethy1 hexyl, nonyl, decyl, lauryl, stearylandsimilar radicals; di-esters of dibasic acids, such asgadipicor sebacic acid with monohydric alcohols, such as hexyl,

octyl, 2-ethyl hexyl or higher alcohols; esters of poly;

ethylene glycols with C -C branched-chain carboxylic" acids; complex esters of polybasic carboxylic acids; polyhYdIICalCOhOlS, mono'basic acids'and/or monohydric alco-' ho1s,such as the well known glycol-centered" or diba'sic acid-centered complex esters of suitable viscosity; phosphoric acid esters or thioesters of aliphatic alcohols or mercaptans of up to about 18 carbon atoms; halocarbon oils, such as polymers of chlorofiuoro alkylenes, e.g. chlorotrifiuoroethylene; organo-siloxanes; sulfite esters; organic carbonates; mercaptals; formals; etc. All these synthetic oils are well known in the artand require'no furtheridentification for those skilled in-the art.

Grease thickeners useful for the preparation of greaseinhibitor concentrates in accordance with the present invention include the metal soaps conventional for grease making, and more particularly the .alkali metal, alkaline earth metal and mixed alkalimetal-alkaline earth metal soaps, e.g. the sodium, potassium, lithium and/ or calcium soaps, of fatty acids, suchzas stearic, oleic, palmitic or the alkali metal of the soap is the same as that of the alkali metal compound inhibitor. For example, a sodasoap is normally used in conjunction with trisodiunrphosphate and a lithium soap in conjunction with lithium hydroxide, etc.

As indicatedrabove," the grease-inhibitor concentrates of the-invention may'contaln as much as 50% by weight or a more of the; inorganic alkali metal-compound inhibitor. Mdre-specifically'pthegrease should contain about 15 by weight of this compound, the'preferred range being about 20-50% by weight of oni theintended use of thelatter. 'The soap-thickener proportion of the grease may likewise vary over a wide rangefbut should, in general, not exceed equimolar proportions as compared to the inhibitor compounds. Mole ratios of inorganic inhibitor to soap of about 10-20 are preferred. Quantities of about 1-25 wt. percent of soap thickener are suitable in most cases, soap concentrations of about 520 wt. percent, based on total grease being preferred. The remainder of the grease is a lubricating oil of the type specified above and may contain small amounts of other conventional additives which are not incompatible with the inorganic inhibitor compound, such as other oxidation inhibitors, extreme pressure agents, oilines's additives, pigments, etc.

The grease-inhibitor concentrates of the invention may be prepared by essentially conventional grease-making procedures. supply the soap constituent of the grease may be heated in a lubricating oil, preferably a mineral lubricating oil, to about 220 F. in a conventional-grease kettle. Caustic soda or other alkali metal hydroxide may be added, preferably as an approximately 50 Be. aqueous solution to' the hot solution to neutralize the acid or This soap stock may then be partially saponify'the fat. dehydrated by further heating to about 300350 F. while stirring. Thereafter, the inorganic inhibitor compound in aqueous solution is added to the hot soap concentrate, dehydrated at 300-400 F. and the remainder of the lubricating oil added. Stirring is continued while the grease is allowed to cool to about 200 F., and the The grease-inhibitor concentrate after cooling may'be homogenized, such as by stirring in a conventional grease kettle; i

As pointed out before, the grease-inhibitor concentrates of the invention may the grease, depending For example, the fatty acid or fat used to be used as lubricating greases without further additions. They may also be used as inhibitor concentrates to be added to other organic oleaginous materials which form organic acids when oxidized by air. When used for the latter purpose, the greases of the invention should be added in amounts sutficient to introduce about 0.1-15 wt. percent, preferably about 0.5- wt. percent, of the alkali metal compound inhibitor into the oleaginous material to be protected against oxidation. Organic oleaginous materials which may be so improved include the hydrocarbon oils of mineral or synthetic origin, their oxygen, halogen, nitrogen, sulfur and/or phosphorus derivatives, the fatty oils and fats, as well as the synthetic lubricating oils mentioned above as dispersants of the grease-inhibitor concentrate of the invention, as well as asphalts, waxes, vegetable oils, etc. No additional solubilizer or dispersing aid is required for an adequate and substantially permanent oxidation-inhibiting eflfect.

An even more important application of the greaseinhibitor concentrates of the invention is their use as inhibitor concentrates for other lubricating greases, one or more constitutents of which tend to react with the alkali metal compound inhibitors as such or which are in some other respect detrimentally affected by the direct addition of the inorganic alkali metal compound inhibitor.

For example, these concentrates may be used to introduce about 01-15 wt. percent, or more, of lithium hydroxide or sodium phosphate or silicate into all types of synthetic oil base greases and all types of greases thickened with non-soap type organic thickeners, such as carbon black, cellulose derivatives, etc. or inorganic thickeners, such as silica gel, amorphous silica, bentonitic and Attapulgus clays and conventional modifications thereof, such as.

bentonites modified by quaternary ammonium bases, Attapulgus clay modified by small amounts of surface active agents; calcium silicate, etc. These inorganic thickeners may contain waterproofing agents, such as various silicone oils, sodium'methyl siliconate; chloromethyl silane; resins, such as alkyd resins; C C primary or secondary alcohols etc.

Regarding suitable methods of incorporating the greaseinhibitor concentrates of the invention into non-compounded organic materials of the type mentionedabove, it is merely necessary to add the grease of the invention to the liquid or liquefied organic material while stirring. Heating is necessary only where required to liquefy the base material. The concentrate is added to the grease which is to be inhibited and the mixture thus obtained may be homogenized by stirring in a grease kettle or by passing through a colloid mill. The addition is preferably carried out at room temperature of, say, 60'80 F., but elevated temperature of up to about 300 F. may be used.

The invention will be best understood from the following description of specific embodiments and working examples thereof.

EXAMPLE I A soda-soap grease containing a large quantity of sodiuni phosphate was prepared having the following commately 0.5%. Two hundred and forty grams of triso=- position:

Percent by weight l2-Hydroxystearic acid 7.0 Candelilla wax 2.8 Sodium hydroxide, anhydrous 2.8 Trisodiurn phosphate, anhydrous 37.0 Mineral oil (V./2l0=ll0 SUS; V.I.=90) 49.0 Phenyl alpha-naphthylamine 1.4

Preparation 0 the grease dium phosphate dodecahydrate were dissolved in an equal weight of water and then added to the soap stock. The soap-salt complex was then partially dehydrated by heating to 300 F., whence the remainder of the mineral oil was added (75 grams). The phenyl alpha-naphthylamine was added at this stage/ Dehydration was then completed by heating the grease to 300 F. In some cases, traces of water may be required to maintain the greaselike consistency. The candelilla wax serves merely as a dispersing agent.

Inspections on thebase grease A grease-inhibitor concentrate was prepared containing sodium phosphate and calcium stearate soap. The composition of this grease was as follows:

Grams Calcium stearate 5 7 Mineral oil 30 N33PO4.9H20

The grease was prepared by adding the sodium phosphate in aqueous solution to the calcium stearate-oil mixture and heating to 300 F. When dehydration was complete, a hard grease was obtained which is useful as an antioxidant.

EXAMPLE HI A lithium stearate grease having the following composition was prepared by heating the ingredients to 400 F.

and casting:

Percent LiOHH O 28.4 Stearic acid 6.8 Mineral oil (V./ 100:300 S.U.S.) 64.8

This grease titrated 27.5% free LiOH.

To show the effectiveness of this .grease as an antioxidant, 4% of the grease was added to a grease containing 9% of a mixed calcium-lithium (:20) hydroxystearate soap. This grease'was evaluated at 250 F. by the dish oxidation test. After 600 hours at this temperature, it is still a light-colored product and shows no oil separation. The same grease. containing no inhibitor concentrate is of brown-black color after 480 hours, showing advanced oxidation, and bleeds a large amount of oil.

EXAMPLE IV containing hydrophilic groups (OH'orNH groups) and' oleophilic groups (alkyl groups). The mixture was heated under pressure to about 300 F. and milled while preventing water losses (grease A). To one portion of this grease A about 2.7 wt. percent of the grease of Example I was added by mixing at room temperature (grease B). To another portion of grease A about 9.3 wt. percent of the grease of Example I- was added by mixing at room temperature (grease C). Into a third portion of grease A there was incorporated about 3.8 wt. percent of anhydrous trisodium phosphate which was dispersed in oil by ball-milling (grease D). Comparative test results obtained with these greases are summarized in Table I below.

Dish oxidation test: 30 grams of grease are placed in a.

2" x 2" x stainless steel dish so that none of the grease touches the edge of the dish. The pans are placed in an oven at 250 F. Periodically color degradation, oil separation, grease consistency and structure are measured. The life of the grease is arbitrarily taken when the grease becomes fluid.

7 EXAMPLE-V "A modifiedbentonitic clay powder prepared by treating bentonite with a .quaternary ammonium alkyl salt in a conventional" manner wasf added to mineraloil Off 1200 S.S.U. at 100F'. and 90 V.I.-along .with about 1.3 wt. percent of acetone based on total composition. "After stirring at room temperature for b hour, the grease was milled (grease E). One-portion of this grease was mixed at room temperature with about 2.8 wt. percent ofthe grease of Example I (grease F). These-greases were tested with the results shown in Table I below.

' EXAMPLE VI Two lubricating greases were prepared'by mixing finely divided amorphous silica 'withmineral oiland passing through a'colloid mill. The mineral oil was a solvent refined distillate having a viscosity of about. 500 S.S.U. at 100 F. and 2. VJ. of 90. The amorphous silica was finely divided water-resistant substantially anhydrous silica (containing 87% Si and 13%- waterproofing agent) manufactured and sold by DuPont under the trade name Du Pont Hydrophobic Silica and described in US. Patent Nos. 2,657,149 and'2,676,148.

---For-aproper: understanding of the data summarizedin: Table I it should be keptin mind that a grease which has hardenedtto' a micro penetration of about 5 as the resultof-soiloxidation and evaporation, will'permit bearing-failurein the --high speed spindle test. It will be noted that grease;-A' which did not contain the grea seinhbitor concentrate of the invention reached a micropen'etriationof 5 after about 700-800 hours at 300 F. while: grease B which contained a small amount of the grease-inhibitor concentrate was still soft enough to lubricate (micropenetration of 12) after about 1200 hours. Similar comparisons favorable to the greases of the in-- vention :may be-ma'de for the other greases listed.

EXAMPLE VIII hydroxystearategrease, substantially in the manner described in Example I. The composition and properties of these" greases are summarized in Table 11 below.

TABLE TIL-EFFECT OF TRISODIUM'PHOSPHATEAQPN4EQPPING POINT AND GREASE HARDENING LIFE Designation 1 .1 2. V 3 4 5 6 7 8 9 Formula, Percent by weight:

12-hydroxystearlc acid 24. 0' '24. 0 24. 0 24. 0 24. 0 24. 0 24. 0 24. 0 24. 0 Candelilla wax 4. 0 4. 0 4.0 4. 0 4.0 i. 0 4. 0 4. 0 4. 0 Sodium hydroxide 3. 2 312 3.2 3. 2 3. 2 3. 2 3. 2 3. 2 3. 2 Tflsodium phosphate 3. 2 6. 4 9. 6 12. 8 16. O 19. 2 25. 6 3S. 4 Mineral oil V./210=110, V.I.-=90 67. 8 165; 6 61. 4 59. 2 55. 0 52.8 49. 6 42. 2 29. 4 Phenyl alpha-naphthy 1. 0- 1'. 0 1.0 1. 0 1. 0

Inspections: V

' Worked penetration 236 215 270 270 214 270 265 207 80 Dropping point, F 380 0 600. 530+ 408 500+ 500+ 500+ 500+ Grease hardening life at 400 F. (hours to a micro penetration of 5) 1 20 215 210 230 170 100 120 Mole ratio of trisodium phosphate to fatty acid M M; M 1 1% 1% 2 3 One of the greases wasmixed at room. temperature with about 19.0 wt. percent ofthe grease of Example I and contained about 9.8 wt. percent of silica (grease G)- The other grease contained about 12 wt. percent of silica and no organic alkali metal compound inhibitor (grease H). These greases were likewise tested as tabu lated below in Table 1.

EXAMPLE v11 TABLE '1.

It will be-observed that the base greasehas a dropping point of 380 F. When the phosphate content is 6%- or higher, thedropping point is raised to about 500 F. Regarding the relationship between grease hardening life at 400 F. and the concentration of the trisodium phos-- phate; it will be observed that there is an optimum' phosphate contentlying in the range of about 6-14%.

EXAMPLE IX' Further experiments were carried out to determine the influence ofoil viscosity on grease stability. For. this purpose. several greases were prepared substantially by the method outlined in Example I using base oils of Composition:

Bentonite $151355?) hrs-:

.43 at 900 hrs 1 Balance of these compositions (4.49%) consists of surface active agents which assist the dispersion of the Attapulgitc in the oil.

a As a dispersion aid. 8 5 grams of grease are packed intoa 204 bearing micro-penetration'ls measured; In general, when the grease reaches a micro-penetration which is then stored at 300 F. in air. 1 At intervals, the grease is removed from the beeringnnd its "etc the bearing 'in which it is the lubricant, will fail.

varying viscosity. The composition and properties of these greases are summarized in Table III below.

cent of a material selected from the group consisting of trisodium phosphate and lithium hydroxide and about TABLE III.-EFFECT OF MINERAL OIL VISCOSITY ON GREASE HARDENING LIFE OF GREASES CONTAINING TRISODIUM PHOSPHATE 1 Designation- 10 11 12 13 14 Formula, percent by weight:

Sodium hydroxide 3- 2.8 3. 0 3. 0 2.

l2-hydroxystearic acid--. 22 20 Double pressed stearlc ac 20 16.7

Trisodium phosphate l1. 5 11. 7 11. 5 11. 5 9. 6

Mineral oi1 V./2l0=65, V.I.=90 2 63. 5 V./210=110, V.I.=90 2 61. 5 63.5 v./21o=140, v.I.=100 3 63.5 V./210=100, V.I.=100 4 69.5

Sodium Sulfonate (63%) 2. 0 2.0 2.0 2. 0 1. 7 Inspections:

Mineral oil viscosity at 210 F., S.U.S. 65 110 110 140 190 Micro penetration at 77 F 40 69 55 85 59 Dropping point, F 498 470+ 448 500+ 500+ Grease hardening life at 400 F., hours 115 212 230 245 250 1 Mol ratio of fatty acid to trisodium phosphate 1:1.

= Solvent extracted and dewaxed.

3 Solvent extracted.

4 Steam reduced residue.

It will be noted that the grease hardening life in- 1 to wt. percent of an alkali metal soap of C to C creased with the viscosity of the base oil up to about fatty acid and a dispersant proportion of a mineral lubri- 140 S.S.U. at 210 F. Further increases in viscosity 25 eating oil, had little effect. It is desirable, therefore, to use base 2. A method according to claim 1, wherein said lubrioils having viscosities of about 130150 S.S.U. at 210 eating grease contains a mixed calcium-lithium soap F. for the greases of the present invention. thickener.

I Wi l be Understood that the i p Oleaginolls 3. A method according to claim 1, wherein said mamaterials prepared in accordance with the invention may 30 t rial i trisodium phosphate. contain other conventional modifiers, such as other anti- 4, A th d according to l i 1, h i id oxidants, e.g. phenyl alpha-naphthylamine; corrosion int ial i lithium hydroxide. hibitors, e.g. sorbitan esters of fatty acids; tackiness agents, eg polyisobutylene of about 1,000 mol. wt.; vis- 3 Ref re e Cit d i the file of this patent cosity index improvers, e.g. polyisobutylene of about 5 15,00020,000 mol. wt.; detergents, e.g. calcium sulfo- UNITFD STATES PATENTS nate, sodium sulfonate, etc; extreme pressure agents, 2,079,051 Sulllvall et y 1937 e.g. sulfurized sperm oil or chlorinated wax; etc. 2,434,539 BfierbOWeF et 1948 The invention is not limited to the specific figures of 2,455,659 Duncan et a1. Dec. 7, 1948 the foregoing examples. The relative proportions of the 2,605,225 Armstrong July 29, 1952 materials used and the reaction conditions may be varied 2,626,896 Dllworth Jan. 27, 1953 Within the limits indicated in the specification to obtain 2,626,399 Abrams Jan. 27, 1953 products of varying characteristics. 2,648,633 Peterson et al Aug. 11, 1953 What is claimed is: 2,684,944 Zajac July 27, 1954 l. A method of inhibiting a lubricating grease against 5 2,738,329 Parry Mar. 13, 1956 oxidation wherein said lubricating grease comprises a 2,748,081 Peterson et a1 May 29, 1956 major proportion of a lubricating oil and a minor grease thickening amount of a calcium soap thickener, which FOREIGN PATENTS method consists of mixing into said grease an amount 160,330 Australia Aug. 7, 1952 sufiicient to inhibit oxidation of said grease of a grease- 850,051 Germany Sept. 22, 1952 inhibitor concentrate comprising about 15 to wt. per- 706,555 Great Britain Mar. 31, 1954 

1. A METHOD OF INHIBITING A LUBRICATING GREASE AGAINST OXIDATION WHEREIN SAID LUBRICATING GREASE COMPRISES A MAJOR PROPORTION OF A LUBRICATING OIL AND A MINOR GREASE THICKENING AMOUNT OF A CALCIUM SOAP THICKENER, WHICH METHOD CONSISTS OF MIXING INTO SAID GREASE AN AMOUNT SUFFICIENT TO INHIBIT OXIDATION OF SAID GREASE OF A GREASEINHIBITOR CONCENTRATE COMPRISING ABOUT 15 TO 80 WT. PERCENT OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF TRISODIUM PHOSPHATE AND LITHIUM HYDROXIDE AND ABOUT 1 TO 25 WT. PERCENT OF AN ALKALI METAL SOAP OF C12 TO C30 FATTY ACID AND A DISPERSANT PROPORTION OF A MINERAL LUBRICATING OIL. 